The present invention generally relates to laser drilling and laser milling and particularly relates to microfilter alignment in a laser drilling system.
Material ablation by pulsed light sources has been studied since the invention of the laser. Etching of polymers by ultraviolet (UV) excimer laser radiation in the early 1980s led to further investigations and developments in micromachining approaches using lasersxe2x80x94spurred by the remarkably small features that can be drilled, milled, and replicated through the use of lasers. A recent article entitled xe2x80x9cPrecise drilling with short pulsed lasersxe2x80x9d (X. Chen and F. Tomoo, High Power Lasers in Manufacturing, Proceedings of the SPIE Vol. 3888, 2000) outlines a number of key considerations in micromachining. Other recent patents of interest include the following:
U.S. Pat. No. 6,266,198, xe2x80x9cConsolidated laser alignment and test station,xe2x80x9d describes a consolidated laser alignment and test station. In exemplary embodiments, equipment sufficient to perform complete dynamic testing and alignment of a laser transceiver unit is provided in one compact arrangement. As a result, cavity-box efficiency testing, dynamic open-interferometer alignment, dynamic open-case alignment, closed-case laser boresighting, and complete laser functionality and diagnostic testing can be carried out efficiently at a single location. Real-time diagnostic feedback relating to beam quality, radiometry, and temporal behavior is provided so that high-precision laser alignments and repairs can be made quickly and cost effectively. Customized test fixtures provide easy access to every level of the transceiver unit under test, and two cameras provide far-field, near-field, wide-field and receiver-field beam viewing. One camera is combined with a pin-hole lens and a quad step-filter optic attenuator to provide a wide-field beamfinder assembly enabling an operator to quickly align the laser under test to the narrower field of the second (diagnostic) camera. The second camera provides near-field and far-field beam viewing, while a radiometer and a pulse detector provide additional diagnostic information. The beamfinder assembly also provides receiver-field laser viewing for receiver-path boresight adjustments. In an exemplary embodiment, the beamfinder assembly includes a quad step-filter constructed from circular wedge filters.
U.S. Pat. No. 6,122,106, xe2x80x9cDisplaced aperture beamsplitter for laser transmitter/receiver opto-mechanical system,xe2x80x9d describes a single aperture opto-mechanical system for transmitting two small-aperture laser beams and a single received laser beam. The two pencil-thin transmitted beams are co-aligned within 150 micro-radians in the same direction but have optical axes that are displaced laterally. An in-coming beam is received along a path that is essentially parallel with the path of the transmitted beams within 500 micro-radians. The small-aperture transmitted beams each pass through a hole in a metal mirror beamsplitter that is positioned to reflect the received light energy at a 90 E angle through a narrow band-pass filter and focused by an aspheric glass lens that directs the received beam energy onto a receiver detector. The beamsplitter has indexing features that provide self-alignment of the beamsplitter to the laser mount.
U.S. Pat. No. 5,991,015, xe2x80x9cBeam monitoring assembly,xe2x80x9d describes a beam monitoring assembly that provides near-field imaging, far-field imaging and power measurements of a laser beam in real-time for alignment and performance verification purposes. The monitoring assembly includes a holographic beam splitter that splits the laser beam from the laser resonator cavity into a series of separate split beams having varying beam powers. One of the split beams is directed to a power meter to measure the power of the beam. One of the split beams is directed to a near-field camera that provides a near-field image of the beam. Another one of the split beams is directed to a heat dump that absorbs and removes the beam""s energy from the assembly. Another one of the split beams is directed to a far-field lens that focuses the split beam onto a far-field camera that provides a far-field image of the beam. The near-field and far-field images of the beam are displayed on an operator control panel in real time. Suitable computer electronics and camera electronics are provided to process the electrical signals from the power meter and the cameras.
Japanese Patent JP62,273,503, xe2x80x9cLaser alignment measuring instrument,xe2x80x9d describes a laser alignment detector including a screen with scale marks, lighting device, partially transmitting mirror which partially transmits rays of light, image pickup element placed on the reflecting optical axis of the mirror, and box body which intercepts outside light and houses the screen, mirror, lighting device, and image pickup element. An incident laser beam passes through an optical filter for adjusting light quantity and reaches a half mirror, which is a partially transmitting mirror. The transmittance of the half mirror is about 30% and a non-reflective coating is performed on one side of the mirror for preventing the ghost of the laser beam. About 50% quantity of the laser beam reflected by the half mirror is absorbed into a box body, which is plated to a black color. The transmitted laser beam hits a screen with scale marks and the laser pattern is monitored by a CCD camera through the half mirror. An optical filter for adjusting light quantity is provided in front of the CCD camera containing an image pickup element and LEDs are provided beside the screen as lighting devices for illuminating the scale marks, so that the scale marks on the screen can be seen with the CCD camera. Therefore, the compact laser alignment-measuring instrument can be obtained.
Ultrafast lasers generate intense laser pulses with durations from roughly 10xe2x88x9211 seconds (10 picoseconds) to 10xe2x88x9214 seconds (10 femtoseconds). Short pulse lasers generate intense laser pulses with durations from roughly 10xe2x88x9210 seconds (100 picoseconds) to 10xe2x88x9211 seconds (10 picoseconds). Along with a wide variety of potential applications for ultrafast and short pulse lasers in medicine, chemistry, and communications, short pulse lasers are also useful in milling or drilling holes in a wide range of materials. In this regard, hole sizes in the sub-micron range are readily drilled by these lasers. High aspect ratio holes are also drilled in hard materials; applications in this regard include cooling channels in turbine blades, nozzles in ink-jet printers, and via holes in printed circuit boards.
Parallel processing of laser-milled holes is a key technique for increasing throughput in laser micromachining. Beamsplitting devices (beamsplitters) such as diffractive optical elements (DOEs) are used in laser micromachining to divide a single beam into multiple beams and thereby achieve parallel machining. However, such use of beamsplitters introduces technical challenges in hole geometry requirements and in the ability to produce consistent, repeatable results. Such challenges need to be overcome in order to maintain consistency and repeatability in laser milling.
The primary advantage of a parallel process laser drilling system over a single beam laser drilling system is the efficiency gain in processing time. Parallel process drilling systems drill many holes in the same amount of time that a single beam laser drilling system drills just one hole. The repeatability and quality of the parallel-processed holes is important to create a product that meets the required specifications. Any variation in beam intensity or in alignment between sub-beams causes a parallel process laser drilling system to drill misshapen holes, creating a product that does not meet specifications.
Alignment of microfilters to the sub-beam pattern is critical in producing a drilled workpiece that meets final specification. The microfilter needs to be adjusted in terms of position and focus to achieve these specifications. However, current methods for adjusting microfilters are complex and time consuming, and therefore not cost efficient.
What is needed is a way to increase the performance of a parallel process laser drilling system by being able to rapidly and optimally align a microfilter within a parallel process laser drilling system when alignment is required. Fullfilling this need requires a way to simultaneously align a plurality of beams with a microfilter in a parallel process laser drilling system and also a way to determine the degree and nature of misalignment of the sub-beams. The present invention provides a solution to these needs.
According to the present invention, a laser drilling system includes an imaging device illuminated by at least two sub-beams of the laser drilling system, including a first sub-beam and a second sub-beam, a microfilter intersecting beam paths of the first sub-beam and the second sub-beam, and a display communicating an image from the imaging device to an operator of the laser drilling system.
A number of advantages are provided with the invention. For example, equalizing the sub-beam intensity and aligning sub-beams through a microfilter increases the performance of a parallel process laser drilling system. A way is also provided to align and confirm alignment of a microfilter in such a drilling system toward an optimal alignment of the sub-beams. Another advantage of the present invention relates to determining the degree and nature of misalignment in a microfilter respective to the sub-beams of a parallel process laser drilling system. The present invention also provides a way to align beams outside of the visible-spectrum (e.g., infrared beams).
The ability to align a microfilter with the sub-beams of a parallel process laser drilling system without disturbing the optical alignment of the other system elements is yet another benefit. Finally, the basic invention provides a way to align a microfilter with the sub-beams of a parallel process laser drilling system with a CCD camera without damaging the CCD camera with the high power laser beams.
In a preferred form of the invention, a further benefit of using a microfilter with a reflective coating is that a way is provided to optimize the contrast between the sub-beams"" incidence location upon the transmissive disks of the microfilter and the sub-beams"" incidence location upon the reflective coating of the microfilter, thus providing an improved alignment means in a parallel process laser drilling system. In a preferred use, print resolution in inkjet printers is also realized when the inkjet nozzles of the printer are manufactured with the benefit of the invention.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.